Aerodynamic rotational stabilization techniques for projectiles

ABSTRACT

A pliant projectile is provided with a plurality of 1-shaped grooves in the circumference thereof. The grooves are at an angle with the axis of the projectile and, in flight, will, through interaction with the air, cause the projectile to rotate about its axis, thereby stabilizing the flight path. The projectile may be provided with an additional stabilizing member extending from its tail which member includes a plurality of tabs each having a fin that can interact with the air, in flight, to add additional rotational forces to the projectile.

This is a continuation-in-part of my provisional application for letterspatent Ser. No. 60/730,345, filed Oct. 27, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to special purpose projectiles, and, morespecifically to novel techniques to significantly improve the accuracyand consistency of projectiles fired from smooth bore weapons, such asshot guns and mortar launchers.

2. Description of the Related Art

U.S. Pat. No. 6,782,828 B2, issued to the present inventor, disclosesnovel techniques for discharging elastomeric projectiles from fire armswithout risk of the soft projectiles jamming or lodging in the barrel ofthe weapon. Although these unique cartridges have been widely acclaimedby both law enforcement and various branches of the government and theDepartment of Defense, better accuracy and consistency, particularly atextended range, were sought after by some of these same users. Borderpatrol, prison guards, wildlife management and control and riot controlofficers in particular, require rounds that they could use at distancesfrom 50 to 100 yards, for successfully engaging a human or animal sizedtarget consistently and meaningfully, without lethality.

As a result of several years of development and testing of this type ofless lethal, very soft projectile, it was recognized that to achievethat range with consistent accuracy, some additional in-flightstabilization techniques would have to be developed. Extensivedevelopment effort has resulted in a preferred embodiment for atechnique and design for what will now be referred to as aerodynamicrotational stabilization or “aerodynamic rifling”.

SUMMARY OF THE INVENTION

A significant reason that rifle and pistol ammunition is extremelyaccurate at close range as well as extended range is the presence ofrifling in the bore of the weapon. Rifling is a series of alternate“lands” and “grooves” that are machined longitudinally into the bore ofthe barrel in a helical pattern. This slight “twist” imparts a spin tothe solid lead or copper projectile as it is forced through the bore ofthe weapon and subsequently provides a remarkable stability to theprojectile in flight.

Because shot guns and mortar launchers, for example, are not providednormally with rifled barrels and the soft, less lethal projectile of theaforementioned and present invention, require minimum contact with asmooth bore for their best performance, it became the challenge toimpart some slight rotation or “spin” to the projectile during flightgiving rise to the term “aerodynamic rifling”.

During the compression or injection molding process of the softelastomeric projectile, a multiplicity of generally “L” shaped groovesare placed at a slight angle to the horizontal axis, around theperiphery of the projectile. As the projectile passes through the air athigh velocity, the raised “lands” which are positioned at a slight anglewith respect to the air stream, cause the projectile to rotate aroundits horizontal axis from the influence of the air stream through whichthe projectile passes.

How and why the projectile rotates is a function of a combination ofmany interrelated factors such as the initial muzzle velocity, thenumber of “lands” and “grooves” on the projectile, the depth of thegrooves and equally important, the angle of the “lands” with respect tothe horizontal axis of the projectile. The optimum angle, however, canonly be determined and is affected by, the values of the otheraforementioned parameters, which may also vary themselves, dependingupon the range required of the round and even the durometer of theelastomeric projectile.

However, the novel feature that contributes most to the aerodynamicrotational performance of the design is the configuration of the riflingprofile itself. In order to allow the air stream maximum access to theangled vertical surfaces of the “lands”, the profile must take more ofan “L” shaped configuration with one surface of the vertical leg of the“L” radiating from the center axis of the projectile and the other legsurface positioned at up to a 90 degree angle with respect to the firstvertical leg surface. This configuration provides maximum access of theair stream to the vertical angled surface of each “land”.

There exists an additional novel feature incumbent with aerodynamicrifling that is only possible with a very soft projectile that isdisclosed in the aforementioned patent and in the present invention. Asstated earlier, the interrelationship of many variables combined innumerous ways, all contribute to the rotation of the projectile as itpasses through the air. One difficulty encountered, especially in thelonger range versions (which require a higher initial velocity), was theincreased aerodynamic drag, resulting from the elevated rotational speedproduced at these higher initial velocities.

With reference to the structure described and shown in the patent, byextending the length of the transfer rod, or by the addition of one ortwo more buffer pads in front of the transfer rod (effecting the sameresult), the projectile, during the initial acceleration phase, ispermitted to elongate even further than normal before its rear portionis contacted by the accelerating front surface of the piston. By thisadditional stretching of the projectile, the original angle of thesurface of the rifling “lands” on the projectile is decreased slightlyduring the projectile's exit from the barrel of the weapon and for aperiod of time during its initial flight to the target, thus reducingits rotational velocity.

During flight, the elastic memory of the projectile causes it toretract, assuming a configuration close to the original angle of therifling. During this same period of time, the projectile's speed isdeteriorating from its original muzzle velocity. Within certain limits,the rotational velocity of the projectile is inversely proportional tothe forward velocity of the projectile. Therefore, as the projectileslows as it approaches target, the more unstable it would become were itnot for the greater stability provided by the increased rotationalvelocity resulting from the restored angle of the rifling.

This unique self compensating feature, although it exists to some extentin all aerodynamic rifling versions, is particularly beneficial, if notrequired, in all extended range configurations of aerodynamic riflingrounds. The unique configuration of the “aerodynamic rifling” providesan additional significant enhancement pertaining to themanufacturability of the projectile.

Normally the design of an injection or rubber compression mold toproduce a sophisticated part such as this would require theincorporation of “slides” in to the mold cavities to facilitate therelease prior to ejection of the finished part from the mold. Slides arecomplicated and expensive and decrease the mold cavity density. Thisprojectile, due in part to the low durometer of the elastomer and inpart due to the modest angle of the rifling, but mostly due to thesubstantial included angle between the two surfaces of the “L”, may beremoved easily from the mold cavity without the aid of slides. Thismoldability significantly increases the production rate and lowers theinitial cost of the molds.

Testing this design in a 12 gauge shotgun with an initial muzzlevelocity of approximately 700 f.p.s. at a range of 75 yards, resulted inmost all projectiles impacting within a man sized target profile—unheardof for a soft elastomeric less lethal shotgun projectile.

An additional feature of this configuration is that the multiplicity of“aerodynamic rifling” grooves around the periphery of the projectile,which, in the preferred embodiment, are approximately 8 or more and, onaverage, 0.040 to 0.060 of an inch or more deep, tend to weaken thecross section of the projectile, allowing it to more readily expandradially upon impact with the target to deliver, at higher velocity,more kinetic energy onto the target body surface while remaining withinacceptable kinetic energy density limits of approximately 100 to 125 ft.lb/sq. in.

While considering additional stabilizing techniques for this projectile,which would further complement the aerodynamic rifling feature, a designfor an improved transfer member for shotguns and other smooth boreweapons evolved. The new design consists of a one piece assemblyincluding the transfer rod, the piston or wad and a multiplicity of tabsadded around the periphery of the rear of the piston.

Affixed to the outer surface of each tab may be vertical fins. The tabscontribute additional in-flight stability to the projectile assembly byeffectively improving the ratio of the length to the diameter (the L/Dratio), which ideally should be approximately 3 to 1. The optionaltapered vertical fins which may be affixed to the top surface of thetabs contribute additional stability. More importantly, these fins canprovide a slight amount of drag stabilization, if needed, for a moreaerodynamically stable projectile.

Also contemplated, but not included in the preferred embodiment, is theconcept of substituting an angled fin for the straight vertical fin.This angled fin can be in lieu of, or in addition to, the “aerodynamicrifling” on the projectile. For example, at very slow projectilevelocities, as in a less lethal mortar round, the additional rotationalforce provided by the angled fins, might optimize its performance aswell as that of small caliber hand gun projectiles where aerodynamicrifling molded into the projectile might not be practical. Again, moldrelease consideration and airstream aerodynamics dictate the shape ofthe solid angled fin.

It should be noted that although all of the aforementioned concepts areprimarily directed toward launching soft projectiles from smooth boreweapons, nothing stated herein precludes launching these type ofprojectiles from rifled bores. It would be highly advantageous, however,to have the induced rotational motion from the aerodynamic riflingcompatible with the twist of the rifled bore.

Forward of the piston section, an annular cup was added to receive therear section of the projectile, which was also lengthened, in a mannerthat more properly contains the back of the projectile during theinitial rapid forward acceleration of the transfer member. This featurereduces the friction between the soft projectile and the shell casingand also provides an improved, less disruptive air flow between thelengthened rear portion of the projectile and the transfer member duringflight. A rim or collar was added around the rear perimeter of therifling on the projectile to provide a more substantial surface withwhich the forward rim portion of the annular cup interfaces during theinitial acceleration phase of the transfer member.

We now have an improved projectile and transfer member, which working inconcert with the novel aerodynamic rifling feature provides a lesslethal 12 gauge point round for law enforcement and the military,capable of both pinpoint accuracy at close range and the ability toengage a man sized target at ranges of from 50 to 100 yards, simply byadjusting the initial muzzle velocity and possibly the durometer of theprojectile.

Although the aerodynamic rifling disclosures in the present inventionwere developed and mainly directed towards applications involving verysoft (25 to 35 Shore “A”) projectiles, it should be noted that the sametechnology might well be applied to the so called “rubber bullets”,that, of necessity, are much harder, being in the range of 60 to 90shore “A” in order to safely transit the barrel of the weapon.

Although the concepts disclosed herein have been primarily directed toless lethal applications, they are all directly applicable to variousother aerodynamic objects, either self propelled or inertia devices,which may benefit from the disclosed methods of aerodynamicstabilization. Applications as widely diversified as toys to less lethaland malodorant mortar rounds are all potential candidates that couldbenefit from this technology.

An additional specific application for this present technology exists inan area referred to as shotgun “slugs” which are single projectiles forshotguns. These heavy projectiles are usually made of lead and are usedfor hunting big game animals and dangerous game such as wild boar andbear. Many states require by law, the use of shotguns and slugs orbuckshot for hunting deer and other seasonal game animals.

Most attempts to improve the accuracy of shotgun slug type projectilesat extended range, has been directed towards inducing some limitedrotational velocity into the projectile prior to its exiting the bore ofthe weapon. The preferred and most pervasive method has been to cast ormold the lead projectile with angular “lands and grooves” around itsperiphery. These rectangular cross sectional shaped “lands” arebasically a mirror image of the rifling on the inside of a rifled gunbarrel. The outside diameter of these “lands” is typically slightlylarger than the inside diameter of a smooth bore of a shot gun barrel,so in transiting the bore, the projectile supposedly is caused torotate. The effectiveness of this approach is questionable because thereis very little improvement in the accuracy of “rifled slugs” over mostnon-rifled slugs in actual practise.

All of the aforementioned technology and design pertaining to lesslethal projectiles is applicable to solid projectiles. The design andspecifications, however, incorporated in a preferred embodiment of asolid projectile will differ from those selected for a low durometer(soft) less lethal projectile. The initial muzzle velocity can be almostthree times that of a less lethal projectile and the number of“grooves”, their depth and angle, will be consequently be affected.

However the technical challenges associated with the successful designof a soft lead or copper slug incorporating “aerodynamic rifling” forsmooth bore shot guns or mortars or the like is much less demanding ifthe techniques disclosed in the present invention are used. A great manyof the overlapping and variable parameters associated with low durometorprojectiles are minimized or completely eliminated with a solidprojectile design.

Accordingly, it is an object of the present invention to provide a lesslethal projectile with improved stability in flight. It is an additionalobject of the invention to provide a soft (low durometer) projectilethat can transit the bore of a weapon without contact and have improvedaccuracy over ranges up to 100 yards. It is a still further object ofthe invention to apply the same principles to metal projectiles forsmooth bore weapons that will exhibit improved in flight stability andgreater accuracy at greater ranges.

The novel features which are characteristic of the invention, both as tostructure and method of operation thereof, together with further objectsand advantages thereof, will be understood from the followingdescription, considered in connection with the accompanying drawings, inwhich the preferred embodiment of the invention is illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for the purpose of illustration and description only, and they arenot intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a projectile according to the presentinvention;

FIG. 2 is a front view of the projectile of FIG. 1;

FIG. 3 is a sectional view of the projectile of FIG. 1 taken along theline 3-3 in the direction of the appended arrows;

FIG. 4 is a transfer rod, suitable for use with the projectile of FIG.1;

FIG. 5 is sectional view of a fin of the transfer rod of FIG. 4, takenalong line 5-5 in the direction of the appended arrows;

FIG. 6 is an alternative embodiment of a transfer rod;

FIG. 7 is a sectional view of a fin of the transfer rod of FIG. 6, takenalong line 7-7 in the direction of the appended arrows; and

FIG. 8 is a partial view of an alternate embodiment of transfer rodfins.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning first to FIG. 1, there is shown a projectile 10 according to apreferred embodiment of the present invention. Molded into the body ofthe projectile 10 are a plurality of L shaped grooves 12 which create aplurality of raised lands 14 around the outer circumference of theprojectile 10. As shown, the grooves 12 and associated lands 14 are atan angle to the axis of the projectile 10.

FIGS. 2 and 3 give a better view of the grooves 12 and the lands 14created when the grooves 12 are formed in the outer surface of theprojectile 10. In flight, the wall of the land 14 provides aerodynamicresistance to the flow of air and causes the projectile 10 to rotate inflight.

Turning next to FIG. 4, there is shown an improved transfer member 20which combines a transfer rod 22 with a piston element 24. Extendingfrom the rear of the piston element 24 is a plurality of tabs 26, eachwith a stabilizing fin 28. FIG. 5 shows the shape of the fin 28 relativeto the tab 26.

FIG. 6 shows an alternative embodiment of an improved transfer member40. In this embodiment, the tabs 42 are provided with angled stabilizingfins 44 that are as wide as the tab 42 at the base of the tab 42 buttaper to a point at the outer end of the tab 42. A cross section of thetab 42, showing the fin 44 is shown in FIG. 7. Yet another embodiment ofa transfer member 50 is shown in FIG. 8. In this embodiment, a pluralityof tabs 52 are provided. Each tab 52 has a fin 54 of uniform width, butwhich angles, diagonally across the width of the tab 52.

Thus there has been shown an improved projectile with a grooved surfacethat can rotate in the flight to a target. The rotation stabilizes theprojectile and increases its accuracy. As part of the improvedprojectile, an improved transfer member is provided which combines atransfer rod with a piston and which can remain with the projectilethroughout the flight. For added stabilization, the piston is providedwith a plurality of stabilizing tabs, each with a fin. The net effect isrotating projectile with finned tabs that help resist pitch and yaw.

The scope of protection of my invention should be limited only by thescope of the claims appended hereto.

1. A pliant projectile to be deployed from a weapon comprising: a. Anose portion; b. A tail portion; and c. A substantially cylindrical bodyportion having a plurality of substantially L-shaped grooves formedtherein, said grooves generally paralleling the cylindrical axis of saidbody portion but at a slight angle thereto.
 2. The pliant projectile ofclaim 1 wherein each of said L-shaped grooves includes a substantiallyradial surface and a substantially circumferential surface, said radialsurface being inclined at an angle with respect to a radius of saidcylindrical body portion.
 3. The pliant projectile of 1 wherein each ofsaid L-shaped grooves includes a substantially radial surface and asubstantially circumferential surface, said circumferential surfacebeing inclined at an angle with respect to the circumference of saidcylindrical body portion.
 4. The pliant projectile of 3 wherein saidradial surface is inclined at an angle with respect to a radius of saidcylindrical body portion.
 5. The pliant projectile of 1 furtherincluding a stabilizing member extending from said tail portion, saidstabilizing member having a plurality of axially extending tabs eachwith a tapered fin orthogonally extending therefrom.
 6. The pliantprojectile of 1 further including a stabilizing member extending fromsaid tail portion, said stabilizing member having a plurality of axiallyextending tabs each with a tapered fin extending therefrom at an acuteangle.
 7. A projectile comprising: a. A nose portion; b. A tail portion;and c. A substantially cylindrical body portion having a plurality ofsubstantially L-shaped grooves formed therein, said grooves generallyparalleling the cylindrical axis of said body portion but at a slightangle thereto.
 8. The projectile of claim 7 wherein each of saidL-shaped grooves includes a substantially radial surface and asubstantially circumferential surface, said radial surface beingsubstantially aligned with a radius of said cylindrical body portion. 9.The projectile of claim 7 wherein each of said L-shaped grooves includesa substantially radial surface and a substantially circumferentialsurface, said radial surface being inclined at an angle with respect toa radius of said cylindrical body portion.
 10. The projectile of claim 7wherein each of said L-shaped grooves includes a substantially radialsurface and a substantially circumferential surface, saidcircumferential surface is substantially orthogonal to a radius of saidcylindrical body portion.
 11. The projectile of claim 7 wherein each ofsaid L-shaped grooves includes a substantially radial surface and asubstantially circumferential surface, said circumferential surface isinclined at an angle to a radius of said cylindrical body portion. 12.The projectile of claim 11 wherein said radial surface is inclined at anangle with respect to a radius of said cylindrical body portion.
 13. Theprojectile of claim 7 further including a stabilizing member extendingfrom said tail portion, said stabilizing member having a plurality ofaxially extending tabs.
 14. The projectile of claim 7 further includinga stabilizing member extending from said tail portion, said stabilizingmember having a plurality of axially extending tabs each with a taperedfin orthogonally extending therefrom.
 15. The projectile of claim 7further including a stabilizing member extending from said tail portion,said stabilizing member having a plurality of axially extending tabseach with a tapered fin extending therefrom at an acute angle.